At 11:24 AM 6/20/01 -0500, Mike Granaas wrote:
>A colleague has approached me about locating references discussing the
>trimming of data, with primary emphasis on psychological research. He is
>primarily interested in books/chapters/articles that emphasize the when
>and how.
>
>I am at a loss on this one and was wondering if anyone could offer a
>coupld of references.
other than what some software programs do ... i don't have ready references
... but, the notion is that for some distributions ... particularly with
some outliers at ONE end ... if you trim say 5% from each end ... it will
reduce the impact on your descriptive stats of the outliers ...
in minitab, there is a trimmed mean that you get as part of the DESCRIBE
command which axes 5% from each end and THEN finds the mean for the middle
90% ...
if you think about it ... you can trim different % values from the ends ...
and, if you did a full trim of 50% from EACH end ... you are at the median!
clearly, the more you trim the data, the narrower the data set is ...
one should only consider trimming in the broader context of are there
outliers and if there are, what (if anything) should we do about them? in
some cases ... you do nothing since, from all accounts, the data are
legitimate values ... but, if you find BAD data at the ends (due to
miskeying, scoring error, etc.), then the first thing is to justify WHAT
values to eliminate if any ...
>Thanks,
>
>Michael
>
>*******************************************************************
>Michael M. Granaas
>Associate Professor [EMAIL PROTECTED]
>Department of Psychology
>University of South Dakota Phone: (605) 677-5295
>Vermillion, SD 57069 FAX: (605) 677-6604
>*******************************************************************
>All views expressed are those of the author and do not necessarily
>reflect those of the University of South Dakota, or the South
>Dakota Board of Regents.
>
>
>
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